Populism as used in anglophone media discourse is vacuous. It has been used to describe movements of right-wing workers with reactionary politics that have been hegemonised by right-wing elites. (US tea party). It has not been applied to centrist (greens) or left-wing movements (“blockade” type politics) despite mass working-class compositions of these movements. Populism is used as a dog-whistle by right wing media, particularly for violent reactionary and fascist organisations despite the non-mass composition of the think tanks that get media attention. In contrast reactionary and fascist mass-organisations of the working class such as /pol/ aren’t described as populist.
The term has no meaning except in the immediate context of a statement by the media. A critical element of the definition is control over a movement by nomenklatura or bourgeois elites; precisely the professional-managerial-technocratic elite which populism is contrasted against. In this case the Guardian is using expert as the antonym of popular. Without any conception that expert advice can be rendered separate to expert rule. So it is contrasting ignorance and expertise. I enjoy my media insulting me.
I would suggest that this is poor terrain to develop theory on.